Automatic alarm system



I NOV. 3, 1936. o. L EKMAN 2,059,510

AUTOMATIC ALARM SYSTEM Filed Dec. 15, 1933 3 Sheets-Sheet 1 NOV. 3, 1936. O L H EKMAN 2,059,510

AUTOMATIC ALARM SYSTEM Filed Dec. 15, 1955 3 Sheets-Sheet 2 Nov. 3, 1936. H EKMAN 2,059,510

AUTOMATIC ALARM SYSTEM Filed Dec. 15, 1935 s Sheets-Sheet 3 Patented Nov. 3, 1936 UITE STATS PATENT OFFIQE Application December 15, 1933, Serial No. 702,629 In Sweden December 1, 1932 29 Claims.

This invention refers to automatic alarm systems having a number of double or multiple wire control circuits, sections, or loops, connected in parallel to a battery and normally closed, each section being provided with means such as, circuit breakers, for breaking the circuit in case of fire or other danger, placed in the localities to be protected.

The object of this invention is to create an automatic alarm system having a perfect selectivity in all cases occurring while being extremely simple and consequently non-expensive and safe in operation.

Another object of this invention is to provide for an earth or ground leakage control by means of a circuit normally closed, containing a normally-energized ground detecting relay.

Another object of this invention is to cause the drop of voltage across similar parts of the wires or conductors of the sections to be substantially equal in all conductors of a section and to make similarly located points substantially equipotential.

Another object of this invention is to render a defect in insulation causing a short-circuiting or leakage between adjacent conductors harmless and protective measures against leakage between the conductors of a section superfluous and to prevent electrolytic corrosion between the conductors and the thermo-contacts of the circuit breakers.

Other objects will be evident from the following specification and claims.

Some embodiments of the invention are shown in the annexed drawings.

Fig. 1 shows a fire alarm system in accordance with this invention.

Figs. 2 and 3 show modifications.

Figs. 4 and 5 show cross sections through double wire cables as used, Fig. 4 being a section on the line IV--IV in Fig. 1, and Fig. 5 a section on the line V-V in Fig. 2.

Fig. 6 shows a two step relay of Fig. 2 in its half-energized position.

Fig. '7 shows the same in its de-energized position.

In Fig. 1 of the drawings I and II indicate two circuits or sections or loops, each comprising two parallel conductors, a, b, and. a number of circuit breakers T (shown in section I only), for instance, fuses, adapted to be melted or conductors a, b, adapted to be otherwise broken substantially simultaneously in case of fire. The sections I and II are connected in parallel to a battery B 5,5 .and extend through the localities to be protected while the parts below line A-A are placed at a central point. The number of sections is arbitrary, although only two sections are illustrated herein for the sake of clearness.

Into each conductor a, b of a section at its end adjacent to the negative pole of the battery B a section relay RIa, RIb, RIIa, RIIb is inserted. Said relays are normally energized having attracted armatures and closed contacts. Those of said contacts which correspond to the a conductors (i. e. contacts of relays R13. and R112.) are connected in series and the contacts of the relays RIb and Bill) are also connected in series. The circuit comprising the contacts of relays RIa, RIIa extends from the positive pole of the battery B through conductor Hill, conductor lill', contacts of relay RIIa, contacts of relay RIa, winding of a normally-energized alarm relay ARa, back to the negative pole of battery B. Similarly the contacts of relays RIb, RIIb are connected in a circuit from the positive pole of battery B, through conductor mu, winding of a second normally-energized alarm relay ARb, contacts of relay RIIb, contacts of relay RIb back to the negative pole of battery B.

The alarm relays ARa, AR}, thus have their armatures normally attracted and contacts open, but when, say, the conductor a. of section I is broken the armature of the relay RIa for that conductor is released. Consequently, the contacts of relay R12. are opened, thus opening the circuit mentioned above through the winding of alarm relay ARa, whose armature is also released and closes its contacts which are connected in series with those of the other alarm relay ARb and with winding of the fire alarm BS in a circuit between the poles of the battery B. This circuit extends from the positive pole of battery B through conductor I00, lower pair of contacts of relay ARb, conductor I02, winding of fire alarm BS, conductor W3, lower pair of contacts of relay ARa, back to the negative pole of battery B. It is, however, evident that this circuit is normally open at the contacts of alarm relays ARa and ARb and is not closed until the armatures of both of said alarm relays have been released at the same time. The indicators (such as annunciators, lamps, etc.) of relays ARa, ARb are shown at ARLa, ARLb in separate circuits through a pair of contacts of said relays, respectively.

Parallel with the sections I, II a circuit is connected to the battery B, which comprises a normally energized earth connection or ground leakage relay JR and an excess current relay OR in seriesand has an earth connection at J. When the armature of JR is released, an indicating lamp JL is lighted. The armature of relay OR is not attracted by the normal current from the battery B through said relay, but if a voltage higher than that of the battery enters the system, for instance, if a conductor contacts with the lighting net, the current through relay OR increases and the armature thereof is attracted and operates an indicator lamp, bell or the like OL.

Each relay should have its own indicator lamp or bell indicating its off normal position as is well known in the art, but for the sake of clearness those indicators are shown for some relays only. Bells or lamps quite similar to 0L and JL may be provided for the other relays. For instance, the contacts of relays AR-a and ARb close circuits for their indicators, when the armatures of said relays are released and close their contacts.

The system described operates as follows:

If only one conductor, say the conductor a, is broken, the armature of the corresponding section relay RIa is released, and disconnects the alarm relay ARa of the a conductor. When ARa closes its contacts, the fault is indicated by its indicator ARLa, but the circuit for the fire alarm BS is broken at the second alarm relay ARb. When both conductors are broken simultaneously, the fire alarm BS is actuated.

If at least one conductor gets a leakage to ground, earth connection relay JR is short-circuited and its armature is released, causing indicator JL to indicate the fault. Too high voltage in the system from an extraneous source of current, which may keep one or more section relays closed though the corresponding conductor is broken, is indicated by excess current relay OR, for which a resistance may be substituted. This resistance or the resistance of OR prevents the section relays from being shortcircuited and a possible false alarm, if an unbroken conductor gets a ground leakage.

Control Switches KsaI, KSaII, KSbI, KSbn are inserted into some or all of the conductors at their ends most remote from the section relays RIa, RIb. If, for instance, KSaI is opened but the armature of RIa is not released, the conductors in the section I are short circuited.

The conductors shall in all correspondingly positioned parts have substantially equal resistance, and, for the apparatus connected in one conductor corresponding apparatus of substantially the same position and resistance shall be inserted into the other conductor. Thus, the drop of voltage across similar lengths of a section is substantially equal in both conductors and similar adjacent points of the conductors are substantially equipotential. Insulation defects punctures possibly causing contact leakage between such adjacent conductors are thus unimportant and do neither produce false alarm nor interfere with the safe function of the plant in case of fire.

Preferably, either (Figs. 1 and 4) or both (Figs. 2 and 5) conductors a, b, have their insulation 0 separately coated with a conducting layer D, such as metal foil or graphite, and said foils are grounded, for instance, via an earth wire E laid into the cable and in contact with said layer as shown also in Figs. 4 and 5. A shortcircuiting between the conductors then causes ground leakage, which is indicated by relay JR. The switches KSaI, KsbI etc. are used to determine that the fault is a contact between conductors and not a ground leakage proper.

In Fig. 1 all relays are normally energized, even the ground leakage relay, which means an increased security of operation in releasing alarm.

In Fig. 2 the section relays of each section are combined with two-step (or three-position) relays R1, Rn having one winding Ta, Tb for each conductor a, b, respectively. Each two-step relay has two contacts 701, kz and when current flows through both windings Ta, Tb, contact k1 is open but contact k2 is closed, as shown in Fig. 2. Upon breaking one conductor either winding Ta, or Tb becomes currentless, the force of attraction decreases and contact 101 closes, as shown in Fig. 6. If also the other conductor of the same section is broken, the coil of the two-step relay is completely de-energized and contact 702 is opened, as shown in Fig. 7. In a main circuit between the poles of the battery B the fault relay FR is connected in series with two branch circuits, connected in parallel to each other and each comprising contact k1 of the corresponding section relay and a fault signal lamp SL1 or SLn. This main circuit extends from the positive pole of battery B through conductor 200, winding of relay FR to point 20l. From that point two branch circuits connected in parallel extend to point 203. One of said branch circuits extends from point 20! through conductor 202, lamp SLII, normally open contact k1 of relay Rn, conductor 204 to point 203. The other of said parallel branch circuits extends from point 20! through conductor 205, lamp SL1, normally open contact k1 of relay R1, conductor 200 to point 203. From point 203 the main circuit extends through conductor 20'! back to the negative pole of battery B. When a conductor, say, the conductor 1) of section II, is broken contact R1 of relay Rn Will be closed (Fig. 6) and closes said circuit through relay FR and the lamp SLn of the section II to indicate the fault and its position. This circuit extends from the positive pole of battery B, through conductor 200, winding of relay FR, conductor 202, lamp SLn, the now closed contact 701 of relay Rn, conductor 204, and conductor 20'! back to the negative pole of battery B. When relay FR is energized in said circuit the contact 703 of relay FR closes the circuit for the fault signal device FEL from the positive pole of battery B, through conductor 200, lamp FEL, contact kg of relay FR, and conductor 208 back to the negative pole of battery B. A circuit extends from the positive pole of the central battery B through conductor 200, winding of a common normally-energized alarm relay AR, normally closed contacts 702 of relay Rn, conductor 209, normally closed contacts 762 of relay R1, conductor 206, conductor 20! back to the negative pole of battery B. Thus, the coil of the alarm relay AR is de-energized, if the contacts k2 of either relay R1, R11 is opened (as a result of the breaking of the two conductors of the same section), and then the contact 704 of relay AR closes the circuit for a local alarm ELD from the positive pole of bat tery B, through conductor 200, alarm ELD, contact k4 of relay AR, and conductor 2l0 back to the negative pole of battery B. Simultaneously, the contact 705 of relay AR releases fire alarm, BS. This circuit extends from the positive pole of battery B, through conductor 200, winding of alarm magnet BS, contact k8, conductor 2,

.contact 705 of relay AR, and conductor 2| 0 back to the negative pole of battery B. The fire alarm magnet BS is controlled by fire alarm relay BR normally energized (via contact 708 of the fire alarm). This circuit extends from the positive pole of battery B, through conductor 200, Winding of BS, contact ks, winding of BR, and conductor 208 back to the negative pole of battery B. Consequently, generally a weak current fiows through said last-mentioned circuit through the windings of relays BR and BS in series, thus controlling the ability of the fire alarm to function. This weak current does not suffice for attracting the lower armature of BS. If, however, the coil of alarm relay AR is de-energized and its armature is released, as described above, the winding of relay BR is short circuited by the current path through conductors 2m and 2H and contacts k5. Then a strong current flows through winding of BS, whose lower armature is attracted and trips the mechanical fire alarm. The indicator (bell) of the relay BR is shown at BRL in an evident local circuit. If the bell BRL rings, it indicates that the fire alarm relay BS cannot function.

The normally energized ground leakage relay JR in a normally closed circuit is connected with the positive pole of the battery B and with an inner point thereof which is grounded at J. If a ground connection occurs in the sections, for instance, at J1, the winding of relay JR is short circuited by the following circuit. The positive pole of battery B through Wire a of section I, ground at J1, ground at J, to negative pole of the battery B. This circuit has a far lower resistance than the high resistance of the winding of relay JR, which, therefore, is shortcircuited causing its armature to be released, as soon as a ground leakage occurs (either a ground leakage proper or a leakage between two wires a, b).

Otherwise the system shown in Fig. 2 is analogous to that shown in Fig. 1 and acts similarly.

The system of Fig. 2 has a minimum of relays, that is, one single relay for each section, a common fault relay, and a common alarm relay.

In Fig. 3 each conductor has its individual section relay Rm, RIb, Rm, RIIb, each having a normally open contact ks and a normally closed contact 767. Contacts ice are connected with one fault indicator RLIa, RLIb, RLIIa, RLIIb each, indicating the fault and its position, when said contactsare closed. Contacts k7 of the two section relays belonging to the same section, for instance, Rm, Eli), are connected in parallel with each other but in series with the corresponding circuit comprising contacts it? of the next section and with alarm relay AR, the latter being thus normally energized across the contacts k7 connected in series and parallel as mentioned. Thus, the main circuit for the alarm relay AR extends from the positive pole of battery B, through conductor 300, winding of relay AR, and conductor 3M to point 302. From this point to point 393 there are two parallel branch circuits, one through contact R7 of relay Rm and the other through contact 767 of relay RIIb. From point 393 the main circuit extends via conductor 364 to point 3%. Between points 305 and 5306 there are two parallel branch circuits, one through contact 107 of relay Rm and the other through contact k7 of relay RIb. From point 3% the main circuit extends via conductor Sfil back to the negative pole of battery B. If a contact k7 in a section is opened, the circuit through alarm relay AR is not broken, and the arma- -have three or more parallel conductors.

ture of the latter is not released until the armatures of both section relays of the same section are released, 1. e. when both contacts 707 "of a section are broken simultaneously. Alarm relay AR actuates fire alarm BS, when its armature is released. Each section or loop I, II has a common switch KS1, KSn, but there may also be individual switches in each conductor.

Ground leakage relay JR in Fig. 3 has its winding inserted into a normally closed circuit across battery B. An inner point of the winding of JR is grounded at J. Thus, relay JR is controlled by the voltage of the battery and its armature is released, when said voltage is too low. It is to be observed that at least the greatest part of the winding of said ground leakage relay JR is inserted between the grounded point of the relay winding and that pole (the positive pole) of the battery B which is connected with that end of the sections which is remotest from the section relays Rn, Rlb, RIIa, Rnb.

If a ground leakage occurs, say at Jr of the wire. a. of section I, this greater (right hand) part of the winding of relay JR will be short circuited by the following circuit. From the positive pole of battery B through wire a of section I, ground at J1, ground at J, the rem-aining minor (left hand) part of the winding JR to the negative pole of battery B. As the greater part of the winding of relay JR is thus short-circuited, the armature of said relay will be released and indicate the fault.

It is to be observed that by grounding of relay JR at the point indicated above the advantage is attained that the high resistance windings of the section relays cannot be included in said short-circuit path for relay JR. If such high resistance win-dings were included, the short circuit path would have too high a resistance and relay JR would not fall off.

Certain modifications may be made in the systems shown and described without exceeding the scope of the invention. Thus, the sections may In some sections, the section relay or relays may be placed at the end of the section next to the positive pole ofthe battery, and in other sections at the end of the section next to the negative pole. Switches, breakers etc. generally used in fire alarm systems may be provided for; conductors a may be connected in series with each other 'and with a common section relay, and this circuit may be connected in parallel with the corresponding conductors b connected in parallel to the battery and having one section relay each, because the resistance of the conductors proper is so low in relation to the resistance of the relays that corresponding points will also in this case be substantially equipotential.

It may be mentioned that individual switches KSaI, KSaII etc. in accordance with Fig. 1 may be used simultaneously with common switches KS1, KSn in accordance with Fig. 3. The diagrams of connections shown in Figs. 1-3 may be used simultaneously in the same system, in some cases even in the same section or loop.

What I claim is:

1. In an automatic fire alarm system, in combination, a battery, a plurality of multiple wire sections connected in parallel to the battery and normally closed, the wires of each section being connected in parallel to said battery, means connected in said wires for breaking the current in case of fire, said means being located in.places to be protected, relay windings connected in said wires between one end of the corresponding section and one and the same pole of said battery, said wires and the apparatus connected therein having substantially the same arrangement and resistance in each wire, thus rendering similar points of the wires of a section of substantially equal potential, contacts operable by said relay windings, and an alarm device in a circuit through said contacts to be released by them.

2. In an automatic fire alarm system, in combination, a number of loops connected in parallel to a battery and normally closed, each loop comprising at least two conductors connected in parallel to said battery, heat-responsive current breakers in said conductors placed in the localities to be protected, individual relays having windings connected with said conductors between one end of the corresponding loop and one and the same pole of said battery, said conductors and the devices connected therein having substantially the same resistance and arrangement within the corresponding loop and similar points of said conductors of a loop being of substantially equal potentials, and an alarm apparatus in a circuit through the contacts of said relays to be released thereby.

3. In an automatic fire alarm, in combination, a central battery, a loop of two equipotential insulated conductors connected in parallel to said battery forming two normally closed circuits, an individual grounded conductive layer on the outside of the insulation of at least one of said conductors, heat-responsive thermo-contacts in said conductors arranged in the localities to be supervised, relays having windings connected with said conductors, and an alarm electrically operated by the contacts of said relays.

4. In an automatic fire alarm system, in combination, a source of electric current, a loop of at least two insulated conductors in a cable connected in parallel to said source of current, an individual conductive coating on the insulation of at least one of said conductors, a grounded bare wire in said cable in contact with said coating, heat-sensitive current breakers in said conductors and located in the rooms to be controlled, individual relays having windings in said loop, said conductors of said cables being of substantially equal potential in all cross sections therethrough, and an alarm device electrically connected with the contacts of said relays to be released therefrom, when all the conductors of said loop are broken simultaneously.

5. In an automatic fire alarm system, in combination, a battery, normally closed multiple conductor sections connected in parallel to said battery, the conductors of each section being also connected in parallel to said battery, heat-actuated breakers for opening said sections in case of fire, normally closed relay windings connected in said sections, some of said relay windings being combined with single relays common to two or more conductors and having as many different positions of operation as the number of relay windings therein, indicators connected with said relays, said conductors of a section and the apparatus connected therein having substantially the same arrangement and resistance in each conductor, thus rendering similar points of the conductors of a section of substantially equal potential, and an alarm device connected with the contacts of said relays to be actuated thereby, when all the conductors of a section are broken.

6. In an automatic fire alarm, in combination, a source of current, normally closed control sections connected in parallel to said source of current, each of said sections consisting of at least two independent insulated conductors connected in parallel to said source of current, all the conductors of each section extending substantially parallel and close to each other, thermostatic means in each section to break all the conductors of the corresponding section substantially simultaneously in case of fire, individual relays in some of said conductors having windings connected between one and the same end of the corresponding section and a pole of said battery, normally closed and normally energized alarm relays having windings in series with the contacts of said individual relays in all similar conductors in those sections which have individual relays for their conductors, and a fire alarm device electrically connected with said alarm relays to be released by them, when they are de-energized at the same time, said alarm device having a winding, all of said alarm relays having their contacts connected in series with each other and with the winding of said fire alarm device, and said conductors of a section and the apparatus inserted therein having substantially the same arrangement and resistance in each conductor, thus rendering similar points of the conductors of a section of substantially equal potential.

7. In an automatic fire alarm system, in combination, a battery, normally closed loop sections connected in parallel to said battery, each section comprising conductors connected in parallel to said battery, all the conductors of each section extending substantially parallel and close together, thermostatic means in each section to break all the conductors of the corresponding section substantially simultaneously in case of fire, individual relays having windings connected into at least some of said conductors between one and the same end of the corresponding section and said battery, and a normally closed contact of each of said individual relays connected in parallel with the same normally closed contact of all other individual relays of the same section, a common alarm relay, having contacts operatively con-:

nected with an alarm to release the latter, when said alarm relay is deenergized, said normally closed contacts being connected in series with each other and with the winding of the common alarm relay, said conductors of a section and all ap-' paratus connected therein having substantially the same resistance and arrangement to cause a substantially equal drop of voltage across similarly situated parts of said conductors of a section.

8. In an automatic alarm system, in combination, a source of direct current, normally closed multiple conductor sections connected in parallel to said source of current, the insulated conductors of each section being also connected in parallel to said source of current, a current breaker in each of said conductors of said sections placed in the localities to be watched over and responsive to the cause of danger to be avoided, individual relays having their windings inserted into the conductors of said sections at one end thereof, control switches inserted at the opposite ends of said sections, an individual conductive grounded coating on the insulation of at least one of said conductors, a fire alarm device electrically operable by the contacts of said relays, and a ground detecting relay electrically connected with said source of current to be responsive to ground leakages.

9. In a fire alarm system, in combination, a

source of current, normally closed multiple conductor sections connected in parallel to said battery, the insulated conductors of eachsection being also connected in parallel to said source of current, fire-actuated current breakers in said sections located in the places to be watched over, individual relays having their windings connected into the conductors of said sections, the conductors of said sections and all apparatus connected therein being so arranged within the section and so constructed that similarly situated points of the conductors of a section are of substantially equal potential, and a fire alarm device electrically operated by the contacts of said relays.

10. In a firealarm system, in combination, a central battery, normally closed multiple conductor sections connected in parallel to said battery, said sections comprising insulated conductors connected in parallel to said battery, fireactuated current breakers in said sections located in the places to be watched over, individual relays having their windings connected into the conductors of said sections at one end thereof, individual control switches inserted into at least some conductors of a section at the opposite end thereof most remote from said relays, the conductors of said sections and all apparatus connected therein being so constructed and arranged that similarly situated points of the conductors of a section are of substantially equal potential, and a fire alarm device electrically operable by the contacts of said relays.

11. In a fire alarm system, in combination, a central battery, normally closed multiple conductor sections connected in parallel to said battery, said sections comprising insulated conductors connected in parallel to said battery, fire-actuated current breakers in said sections located in the places to be watched over, individual relays having windings connected into the conductors of said sections at one end thereof, switches common to several conductors of a section connected therein at the end thereof most remote from said relays, the conductors of said sections and all apparatus connected therein being constructed and arranged to render similarly situated points of the conductors of a section of substantially equal potential, and a fire alarm device electrically operable by the contacts of said relays to be released by them.

12. In a fire alarm system, in combination, a central battery, normally closed multiple conductor sections connected in parallel to said battery, the conductors of each section also being connected in parallel to said battery, all the conductors of each section extending substantially parallel to each other and close together, thermostatic means in each section to break all the conductors of the corresponding section substantially simultaneously in case of fire, section relays having windings inserted into the conductors of said sections, a common alarm relay, and normally closed circuits, comprising break contacts of said section relays of the similar conductors of said sections, said break contacts being connected in series with each other, said circuits comprising said section relay break contacts con nected in series being for different conductors connected in parallel with each other and in series with said battery and with the winding of said common alarm relay, all conductors of a section and the apparatus connected therein having substantially the same arrangement and resistance in each conductor of the corresponding section, thus rend ring similar points of the conductors of a section of substantially equal potential.

13. In a fire alarm plant, in combination, a source of current, normally closed sections connected to said source, some of said sections consisting of at least two conductors connected in parallel to said source of current and extending substantially parallel to each other and close together, insulations on said conductors, a grounded conductive individual layer on the outside of the insulation of a conductor of a section, fire-actuated current breakers connected in said conductors for breaking all conductors of a section substantially simultaneously and arranged in the localities to be protected, an indicator electrically connected with said sections to give one indication if either conductor of a section is broken and another indication if all conductors of a section brok n, a ground leakage relay having its winding connected with said source of current, and a fire alarm device electrically and operatively connected with said current breakers to be released thereby in case of fire.

14. In a fire alarm system, in combination, a battery, a plurality of normally closed multiple wire sections connected in parallel to said battery, the wires of each section being also connected in parallel to said battery and extending substantially parallel to each other and close together, means connected in each of said wires for breaking the current therein in case of fire and located in the places to be protected, relay windings connected into each of said wires between one end of the corresponding section and one and the same pole of said battery, said wires and the apparatus connected therein having substantially the same arrangement and resistance respectively in each wire, thus rendering similar points of the wires of a section of substantially equal potential, contacts in said relays adapted to be actuated by the windings thereof, and an alarm device in a circuit through said contacts to be released therefrom at the simultaneous breaking of the current through all the wires of a section.

15. In an automatic alarm system, in combination, a source of direct current, insulated wires 1 connected across said source of current to form loops located in the places to be protected, a current breaker connected in each of said wires responsive to the cause of danger to be avoided, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, an individual conductive grounded coating on the insulation of at least one of said wires, and a ground detecting relay electrically and operatively connected with said source of current to be responsive to ground leakages.

16. In an automatic alarm system, in combination, a source of direct current, insulate-d wires connected across said source of current to form loops located in the places to be protected, a current breaker in each of saidwires responsive to the cause of danger to be avoided, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, an

individual conductive grounded coating on the a current breaker in said loop responsive to the cause of danger to be avoided, a relay having its winding connected in series with said loop, an indicator operatively connected with the contacts of said relay to be actuated thereby, an alarm apparatus electrically connected with said loop to be actuated when said loop is broken, a normally energized ground detecting relay in a normally closed circuit between two points of said source of current, said ground detecting relay having its armature normally attracted, and a ground connection to an intermediate point of the circuit of said ground detecting relay.

18. An automatic alarm system comprising, in combination, a source of electric current, a loop of two insulated conductors connnected in parallel to said source of current, said conductors of a loop extending close together and parallel to each other, a current-breaker in each of said conductors placed in the locality to be watched over and responsive to the cause of danger to be avoided, a relay winding in each of said conductors,said conductors and all the devices inserted therein having substantially similar resistance and arrangement within said loop in relation to the poles of said source of current and similar points of said conductors being thus substantially equipotential, at least one contact adapted to be operated by said relay windings, and an alarm apparatus in a circuit through said contact releasable by the joint action of said relay windings.

19. An automatic alarm system, comprising, in combination, a source of electric current, a loop of two insulated conductors connected in parallel to said source of current, said two conductors extending substantially parallel to each other and close together, a current-breaker in each of said conductors placed in the locality to be supervised, said current breaker being responsive to the cause of danger against which said locality is to be protected, a relay winding in each of said conductors, said conductors and all the devices inserted therein having substantially the same resistance and arrangement within said loop to render similarly situated points of said conductors substantially equipotential, at least one contact in the magnetic field of said relay windings adapted to be actuated thereby, an indicator electrically connected with said conductors and arranged to give one indication if either conductor is broken and another indication if both conductors are broken, a grounded conductive individual layer on the outside of the insulation of one of said conductors, a ground relay having its winding connected to said battery, and an alarm in a circuit through said contact.

20. In an automatic alarm system, in combination, a battery, a loop of insulated wire connected across said battery and located in the place to be watched over, a current breaker in said loop responsive to the cause of danger to be warned against, a relay having its winding connected in series with said loop, an indicator operatively connected with the contacts of said relay to be actuated thereby, an alarm apparatus electrically connected with said loop to be actuated when said loop is broken, an excess current relay, a ground detecting relay, the windings of said excess current relay and said ground detecting relay being connected in series in a normally closed circuit between two points of said battery, and a ground connection to said circuit from a point between the winding of said excess current relay and that point of said battery to which the winding of said ground detecting relay is directly connected.

21. In an automatic alarm system, in combination, a battery, insulated wires connected across said battery to form loops located in the places to be protected, a current breaker in said wires responsive to the cause of danger to be" avoided, an alarm apparatus electrically connect ed with said loops to be actuated when one of said loops is broken, an individual conductive grounded coating on the insulation of at least one of said wires, an excess current relay, a normally energized ground connection relay having its winding in series with the winding of said excess current relay in a normally closed circuit between two points of said battery, and a ground connection to said circuit from a point between said excess current relay and that point of said battery to which said ground connection relay is directly connected.

22. In an automatic alarm system, in combination, a battery, insulated wires connected across said battery to form loops located in the places to be protected, a current breaker in said wires responsive to the cause of danger to be protected against, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, a normally energized ground leakage relay having its winding in a normally closed circuit between the poles of said battery, the armature of said ground leakage relay being normally attracted, a ground connection to an inner point of the winding of said ground leakage relay, and an individual conductive grounded coating on the insulation of at least one of said wires.

23. In an automatic fire alarm system, in combination, a battery. insulated wires connected across said battery to form loops located in the places to be protected, section relays having their windings inserted into said loops at one end, a current breaker in said wires responsive to the cause of danger to be protected against,

an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, a normally energized ground leakage relay having its winding inserted into a normally closed circuit between two points of said battery, and a ground connection to a point of said circuit, at least the greatest part of the winding of said ground leakage relay being inserted between said grounded point and that pole of said battery which is connected with that end of said loops which is most remote from said section relays.

24. In an automatic alarm system, in combination, a battery for direct current, insulated wires connected across said battery to form loops located in the places to be protected, a current breaker in said wires responsive to the cause of danger, against which protection is sought, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, a resistance, a normally energized ground leakage relay having its winding connected in series with the winding of said resistance in a normally closed circuit extending between two points of said battery, the armature of said relay being normally attracted, and a ground connection from a point between said resistance and that point of said battery to which said ground leakage relay is directly connected.

25. In an automatic electric protection system, in combination, a source of direct current, a normally closed loop of insulated conductors connected to said source of current, said conductors extending close together and parallel to each other in the locality to be watched over, a current breaker in each insulated conductor of said loop and placed in said locality and responsive to the cause of danger, against which protection is sought, and an alarm apparatus electrically connected with said conductors to be actuated when all conductors of said loops are broken simultaneously, said conductors and all devices inserted therein having substantially similar resistance and arrangement and similar points of said conductors being substantially equipotential.

26. In an automatic electric protection system, in combination, a battery, multiple wire sections connected to said battery and normally closed, the wires of each section being insulated and connected in parallel to each other and extending close together, a current breaker in each of said wires and responsive to the cause of danger against which protection is sought, said current breakers being located in places to be protected, relay windings connected in said wires at one end of the corresponding section, said wires and the apparatus connected therein having substantially the same arrangement and resistance in each wire, thus rendering similar points of the wires of a section of substantially equal potential, contacts operable by said relay windings, and a protective device in a circuit through said contacts to be released by them, when all wires of a section are broken simultaneously.

27. An automatic alarm system, comprising, in combination, a source of direct current, insulated conductors connected in parallel to said source of current to form loops placed in the locality to be watched over, a current breaker in each of said conductors and responsive to the cause of danger, for which alarm is to be raised, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, a ground detecting relay having its winding in a permanently closed circuit without any movable contacts between two points of said source of current, said relay having its armature normally attracted, and a permanent ground connection to a point of said permanently closed circuit.

28. In an automatic alarm system, in combination, a battery for direct current, insulated conductors connected in parallel to said battery to form loops placed in the locality to be Watched over, a current breaker in each of said conductors and responsive to the cause of danger, for which alarm is to be raised, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, a ground detecting relay having its winding in a normally closed circuit between the middle point of said battery and another point thereof, said relay having its armature normally attracted, and a normal ground connection to the middle point of said battery.

29. In an automatic alarm system, in combination, a battery, insulated wires connected across said battery to form loops located in the places to be watched over, current breakers in said wires responsive to the cause of danger to be protected against, an alarm apparatus electrically connected with said loops to be actuated when one of said loops is broken, a ground detector relay having its winding in a normally closed circuit between two points of said battery, the armature of said relay being normally attracted, and a permanent ground connection to an inner point of the winding of said relay.

OLOF INGEMAR HARALD EKMAN. 

